Lung cancer is the second most prevalent cancer in the United States and is the most lethal(4). Over 31 million patients in the United States (US) are at high risk for the development of lung cancer, primarily due to a smoking history. Approximately 160,000 US patients die of lung cancer each year(4). Many attempts have been made to develop screening procedures for lung cancer. Traditional cytological methods based on sputum or bronchial wash specimens have been shown to be relatively insensitive, with only about 40-60% of patients with cancer having positive results and the majority of those being from endobronchial squamous carcinomas(5, 8, 7). One bright spot related to the cytology examination is the relatively high positive predictive value of this procedure—generally above 98% —meaning that a positive test is a reliable indicator of disease(7).
The Centers for Medicare/Medicaid Services (CMS) has recently approved reimbursement coverage for low dose CT radiographic scanning (LDCT) for lung cancer screening in highest risk patients(8), and the US Preventive Services Task Force and a number of other professional and advocacy organizations have made recommendations for screening in high risk populations(9,10). Results of the National lung Cancer Screening Trial showed that the use of LDCT can decrease the mortality from lung cancer by 20% compared to conventional chest x-ray(10). Although sensitive for the detection of pulmonary neoplasia (after three consecutive LDCT scans), LDCT has low specificity with false positive results in as high as 96% of patients with a nodule, leading to low positive predictive values(11). In addition, the cost and morbidity/mortality associated with continued surveillance and interventional follow-up must be accounted for, particularly in the false positive population(12). The addition of a non-invasive triage test (such as an early lung cancer detection test) with much higher specificity, therefore, has potential in managing patients who test positive with LDCT examinations. In addition, if the test's sensitivity is also high, then it has the potential to be useful as an independent primary lung cancer screening test as well.
In a related technology, automated and semi-automated algorithmic classifiers based on 2-dimensional morphologic parameters have been in wide clinical use since the 1990's for cervical cytology specimens. One such device is now being marketed as the FocalPoint Primary Screening System (Becton-Dickinson, Franklin Lakes, N.J.(1, 2). The classifiers of the FocalPoint were trained on human evaluation of cells in a labelling process which then informed the algorithmic classifiers, allowing newly presented cells (and cases) to be given probabilities of abnormality. Individual cells and/or cases falling above designated score thresholds are at much higher risk for being abnormal than are those falling below the threshold and can therefore be selected on that basis for focused review by cytologists(1, 2).
Extension of this concept to 3-dimensional morphometric analysis provides the potential for a significantly greater number of measured parameters that are statistically robust and, hence, improve accuracy and clinical performance. Three-dimensional analysis provides much higher resolution of cellular and sub-cellular intricacies than can the currently used cytology devices(3). Given the high morbidity of lung cancer, there is a need for a lung cancer detection test for the detection of lung cancer in its early stages. Such a lung cancer detection test has both the potential for use as a primary screener for lung cancer and also as a test to use adjunctively with LDCT to reduce false positives and costs of screening by LDCT alone.
In pursuit of such an early lung cancer detection system, advances in 3D imaging of biological cells using optical tomography have been developed by Nelson as disclosed, for example, in U.S. Pat. No. 6,522,775, issued Feb. 18, 2003, and entitled “Apparatus and Method for Imaging Small Objects in a Flow Stream Using Optical Tomography,” the full disclosure of which is incorporated by reference. Further major developments in the field are taught in Fauver et al., U.S. Pat. No. 7,738,945, issued Jun. 15, 2010, entitled “Method and Apparatus for Pseudo-projection Formation for Optical Tomography,” (Fauver '945) and Fauver et al., U.S. Pat. No. 7,907,765, issued Mar. 15, 2011, entitled “Focal Plane Tracking for Optical Microtomography,” (Fauver '765) the full disclosures of Fauver '945 and Fauver '765 are also incorporated by reference. Building on the teachings therein an early lung cancer detection technology has been developed by VisionGate, Inc., Phoenix, Ariz. to provide measurement advantages that have the potential to greatly improve the operating characteristics of conventional morphologic cytology analyses. New systems and methods related to such an early lung cancer detection test are described herein.
Processing in such an optical tomography system begins with specimen preparation. Typically, specimens taken from a patient are received from a hospital or clinic and processed to remove non-diagnostic elements, fixed and then stained. Stained specimens are then mixed with an optical gel, inserted into a microcapillary tube. Images of objects, such as cells, in the specimen are produced using an optical tomography system. The resultant images comprise a set of extended depth of field images from differing perspectives called “pseudo-projection images.” The set of pseudo-projection images can be reconstructed using backprojection and filtering techniques to yield a 3D reconstruction of a cell of interest. Having isometric or roughly equal resolution in all three dimensions is an advantage in 3D tomographic cell imaging, especially for quantitative image analysis.
The 3D reconstruction then remains available for analysis in order to enable the quantification and the determination of the location of structures, molecules or molecular probes of interest. An object such as a biological cell may be labeled with at least one stain or tagged molecular probe, and the measured amount and location of this biomarker may yield important information about the disease state of the cell, including, but not limited to, various cancers such as lung, breast, prostate, cervical, stomach and pancreatic cancers.
Unfortunately, currently available testing techniques are hampered by the lack of a method to determine if the specimen has been sufficiently analyzed. In the present invention it has been discovered that, since tumor or abnormal cells shed from the epithelium of a given organ system along with normal cells, these normal cells provide an excellent marker to determine if the specimen has been sufficiently sampled. Using the novel techniques disclosed herein, specimens meeting these conditions are determined to be adequate specimens.